1. Field of the Invention
The present invention relates to a process of manufacturing electronic devices, particularly, Schottky diodes, employing vapor-phase diamond synthesis.
2. Description of the Prior Art
In forming a diamond film through vapor-phase synthesis, a boron-doped (B-doped) p-type diamond film is obtained by doping with boron, i.e., a metallic element of group III. B-doped p-type diamond films are expected to form Schottky diodes having excellent heat and radiation resistance, which has never been achieved by conventional Schottky diodes produced with Si and GaAs. It is also expected that other electronic devices having excellent characteristics can be fabricated using diamond films.
A Schottky diode has been reported, as shown in FIG. 6, in 1989-nen Shunki Oyo Butsuri Gakkai Yokoshu, 2a-N-7 No. 2. This Schottky diode is formed by depositing a B-doped p-type polycrystalline diamond film a on a p-type Si substrate b (the diamond film was prepared using diborane (B.sub.2 H.sub.6) and a 5% CO gas diluted by H.sub.2). On the back side of the Si substrate, an In electrode c which has an ohmic characteristic. An Al needle electrode d is placed on the B-doped p-type polycrystalline diamond film a. This point contact electrode is a Schottky characteristic. As shown in FIG. 7, this Schottky diode prevents a flow of electric current when a positive voltage is applied to the Al needle electrode d, whereas it permits a flow of electric current, when a negative voltage is applied to the Al needle.
The aforementioned paper also reports that a device employing a p-type semiconductor diamond film deposited using a source gas of B.sub.2 H.sub.6 and a 0.5% CH.sub.4 diluted by H.sub.2 exhibits a current-to-voltage (I-V) characteristic as shown in FIG. 8 and does not have Schottky characteristics.
A study of a Schottky diode shown in FIG. 9 has been reported in Journal of Applied Physics, Vol. 65, No. 5, pp. 2139-2414 (1989). This Schottky diode is formed by depositing a polycrystalline diamond film a' on a p-type (100)Si substrate b' having a resistivity in the range of 0.01 to 0.1 .OMEGA..cm (the diamond film was prepared by a microwave plasma CVD process using CH.sub.4 diluted by H.sub.2 as a source gas). An ohmic contact electrode c' is attached on the backside of the substrate, and an Au electrode d' of a diameter of 0.1 cm and a thickness in the range of 140 to 500 .ANG. is deposited on the polycrystalline diamond film a'. The I-V characteristic is shown in FIG. 10.